From 5676acad9e0b530aae507e0b1482cc87c949b762 Mon Sep 17 00:00:00 2001
From: Wei Ding <wei.ding2@amd.com>
Date: Thu, 12 Oct 2017 19:37:14 +0000
Subject: Implement custom lowering for ISD::CTTZ_ZERO_UNDEF and ISD::CTTZ.

Differential Revision: http://reviews.llvm.org/D37348

llvm-svn: 315610
---
 llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

(limited to 'llvm/lib/CodeGen/SelectionDAG')

diff --git a/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
index 3d320a9dda7..bbee69fb656 100644
--- a/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
@@ -2773,7 +2773,7 @@ SDValue SelectionDAGLegalize::ExpandBitCount(unsigned Opc, SDValue Op,
     return DAG.getNode(ISD::CTLZ, dl, Op.getValueType(), Op);
   case ISD::CTLZ: {
     EVT VT = Op.getValueType();
-    unsigned len = VT.getSizeInBits();
+    unsigned Len = VT.getSizeInBits();
 
     if (TLI.isOperationLegalOrCustom(ISD::CTLZ_ZERO_UNDEF, VT)) {
       EVT SetCCVT = getSetCCResultType(VT);
@@ -2781,7 +2781,7 @@ SDValue SelectionDAGLegalize::ExpandBitCount(unsigned Opc, SDValue Op,
       SDValue Zero = DAG.getConstant(0, dl, VT);
       SDValue SrcIsZero = DAG.getSetCC(dl, SetCCVT, Op, Zero, ISD::SETEQ);
       return DAG.getNode(ISD::SELECT, dl, VT, SrcIsZero,
-                         DAG.getConstant(len, dl, VT), CTLZ);
+                         DAG.getConstant(Len, dl, VT), CTLZ);
     }
 
     // for now, we do this:
@@ -2794,7 +2794,7 @@ SDValue SelectionDAGLegalize::ExpandBitCount(unsigned Opc, SDValue Op,
     //
     // Ref: "Hacker's Delight" by Henry Warren
     EVT ShVT = TLI.getShiftAmountTy(VT, DAG.getDataLayout());
-    for (unsigned i = 0; (1U << i) <= (len / 2); ++i) {
+    for (unsigned i = 0; (1U << i) <= (Len / 2); ++i) {
       SDValue Tmp3 = DAG.getConstant(1ULL << i, dl, ShVT);
       Op = DAG.getNode(ISD::OR, dl, VT, Op,
                        DAG.getNode(ISD::SRL, dl, VT, Op, Tmp3));
@@ -2806,11 +2806,22 @@ SDValue SelectionDAGLegalize::ExpandBitCount(unsigned Opc, SDValue Op,
     // This trivially expands to CTTZ.
     return DAG.getNode(ISD::CTTZ, dl, Op.getValueType(), Op);
   case ISD::CTTZ: {
+    EVT VT = Op.getValueType();
+    unsigned Len = VT.getSizeInBits();
+
+    if (TLI.isOperationLegalOrCustom(ISD::CTTZ_ZERO_UNDEF, VT)) {
+      EVT SetCCVT = getSetCCResultType(VT);
+      SDValue CTTZ = DAG.getNode(ISD::CTTZ_ZERO_UNDEF, dl, VT, Op);
+      SDValue Zero = DAG.getConstant(0, dl, VT);
+      SDValue SrcIsZero = DAG.getSetCC(dl, SetCCVT, Op, Zero, ISD::SETEQ);
+      return DAG.getNode(ISD::SELECT, dl, VT, SrcIsZero,
+                         DAG.getConstant(Len, dl, VT), CTTZ);
+    }
+
     // for now, we use: { return popcount(~x & (x - 1)); }
     // unless the target has ctlz but not ctpop, in which case we use:
     // { return 32 - nlz(~x & (x-1)); }
     // Ref: "Hacker's Delight" by Henry Warren
-    EVT VT = Op.getValueType();
     SDValue Tmp3 = DAG.getNode(ISD::AND, dl, VT,
                                DAG.getNOT(dl, Op, VT),
                                DAG.getNode(ISD::SUB, dl, VT, Op,
-- 
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